Radiotelephone station identifying system



June 3, 1952 F. S. ENTZ ET AL RADIOTELEPHONE STATI-ON IDENTIFYING SYSTEM 1o sheets-sheet 1 Filed Deo. 30, 1948 June 3 1952 F. s. ENTz ETAL 2,599,097

RADIOTELEPHONE STATION IDENTIFYING SYSTEM y Filed Dec. zo, 1948 1o sheets-sheet 2 E5. E/vrz N/5MG R. o. .sof-FEL ATTORNEY June 3, 1952 F. s. ENTz ET AL 2,599,097

RADIOTELEPHONE STA'VIION IDENTIFYING SYSTEM ,Filed Dec. 50, 1948 l0 Sheets-Sheet 3 7- Q F 5. N72 Mfg 'O 5 R. 0. SOI-'FEL A TTORNE V June 3, 1952 l l F. s. ENTz ETAL 2,599,097

RADIOTELEPHONE STATION TDENTTFYING SYSTEM Filed'neo. 5o, 194s 1o sheets-sheet 4 E s. .EA/rz N5/Vm R. o. sof-'FEL ATTORNEY FIG. 4

June 3, 1952 F. s. ENTZ ETAL 2,599,097

RABIOTELEPHONE STATION IDENTIFYING SYSTEM Filed Deo. 30, 1948 v 10 Sheets-Sheet 5 llllll IIIIIH Lr) N IN VEN TORS F' s ENTZ ATTORNEV R. 0. SOI-'FEL June 3, 1952 F. S. ENTZ ET AL RADIOTELEPHONE STATION IDENTIFYING SYSTEM Filed Deo. 50, 1948 10 Sheets-Sheet 6 L V. W No m ES T 5.o. W A ER. @la

/NVENTORS June 3, 1952 F, s. ENTz ETAL 2,599,097

RADIOTELEPHONE STATION DENTIFYING SYSTEM Filed Dec. 30, 1948 y l0 Sheets-SheetI 7 s. ENTZ Mg/NTO R. o. sof-FEL ATTORNEY June 3, 1952 F, s, ENTZ ET AL 2,599,097

RADIOTELEPHONE STATION IDENTIFYING SYSTEM Filed Dec. 30, 1948 l0 Sheets-Sheet 8 l\ ii MJ E s. E/vrz Ng-cfm R. o. son-EL ATTORNEY June 3, 1952 F. s. ENTz ET AL 2,599,097

RADIOTELEPHONE STATION DENTIFYING SYSTEM Filled Dec. so, 194s 1o sheets-sheet 9 fs. E/vrz Wm R. o. sof-'FEL JVM/WW# A 7' TOR/VEV Patented June 3, 1952 RADIOTELEPHONE STATION IDENTIFYING SYSTEM Ferdinand S. Entz, Mount Kisco, and Robert 0.

Soffel, Hastings on Hudson, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 30, 1948, Serial No. 68,348

17 Claims. 1

and D. F. Huth-R. O. Soffel, Serial No. 56,186, Y

nled October 23, 1948. This invention relates speciiically to means for identifying any mobile station.

An object of the invention is to provide a system in which any one or more of a large number of outlying stations interconnected by a common transmission medium may be selectively signaled from a calling station, and an identifying signal automatically returned to the calling station to indicate that the called station, or stations, has been signaled.

Another object of the invention is to register at the outlying called station, or stations, a positive indication that a calling signal has been received thereat, even though the outlying stations may be unattended when the call is received.

Still another object of the invention is to provide positive identication at a central ofce station of any outlying party line station which may originate a call.

Although the invention may be 'employed in any communication or signaling system, the preferred embodiment in which the invention is here illustrated is a mobile radio telephone system.

As specifically applied to the preferred embodiment of the invention in a mobile radio telephone system, one ofthe objects is to provide a selective 'signaling system which will return a positive indication to the xed land station that the called subscribers mobile station has been signaled even though 'the mobile subscriber is not in attendance at the time. Such an automatic return indication, which has not been availbetween steel reinforced buildings which may effectively shield the mobile station from receiving the calling signal during a portion of the calling period. Obviously, it is desirable to remove the calling signal from the land transmitter as soon as the mobile station has been signaled in order that -conversation may be commenced Without unnecessary delay.

Such positive indication at the central oillce that the called mobile subscribers station has been signaled is especially desirable in the matter of calling a mobile subscriber who is traveling along a highway between -distant urban areas, as in this case the operator generally has to attempt the call through a number of different transmitting stations successively until a transmitter is located which is Within signaling range of the mobile station. As the mobile subscriber may have stopped and temporarily left his car or truck at any point along his route of travel just at a time when his mobile station is called, the mobile service operator heretofore has had no means of knowing When the car was signaled and under such -circumstances she has continued to search by applying the calling signal to successive transmitters along the route. With the present invention, such prolonged searching for a mobile station is avoided since the invention provides a positive return indication to the central olice that the mobile station has been reached and signaled even though no one is in attendance at the mobile station when the signall is there received. By providing a signal lamp, or othersuitable indicator, together with a lock-up arrangement at the mobile station, the subscriber is given an indication that his station was called during his absence. The use of a gas discharge lampV or other device of low power consumption provides this indication at the mobile station during prolonged periods of unattendan-ce without imposing excessive drain upon the' mobile station battery.

Another object of the invention as adapted to the preferred embodiment is to provide at the central oflice or fixed land station a positive identication of any mobile station originating a call. This is of considerable importance to the telephone company providing mobile radio service since identication in such cases is necessary for proper billing of the toll charges which may be involved. Heretofore, the mobile service operator has had to ask the mobile subscriber who originated a call to identify himself or the station from which he was calling, as there has been no other way of determining which one of a large shown innig.' 1.

wherebyeach mobilerstation upon being putinto` operation by or on behalf of a subscriber originating a call, automatically transmits a station identifying signal Which may be received and positively identified at the central oii'ice.

An understanding of the circuit arrangements contemplated by the invention, and better appre-. ciation of the various features and, advantages thereof, is to be gained from a study of the Aaccompanying drawings illustrating .a preferred Figi'villustrates a display circuit to indicate whichsignai currents are selected by the register translatorof Fig. 4, and also to identify a mobile station originating a call;

4 corded in a register circuit included Within the dial pulse sender. Contacts on the register relays convert the four-digit decimal number into a combination of four out of thirty audio frequencies in the manner disclosed by aforesaid copending4 application of Hoth-Soffel Serial No. 56,186. These frequencies are transmitted over lead group H33 to the combiner circuit No. 4 where they are ampliiied and combined through hybrid coils from whence Vtheyare transmitted over lead group I G4 through equipment in the control unit 2 over lead group |05 to radio transmitter 5 where they Y are used to modulate the carrier frequency.

Fig. l6z illustratesa combiner circuit for combining the selected plurality of different frequency signalcurrentsvinto a unitary station calling signal;

Fig. V'7; illustrates. switching control arrangements lat a central office or land station control terminal;

Figs. 8 and 9 taken together illustrate a multifrequency vtranslator for converting a plurality of simultaneously received signal currents of different frequencies into their corresponding decimal code equivalent;4

Fig.` 10 illustrates-:a circuit for switching arrangements. at amabile radio telephone station adapted "for twofwayccmmunic'ation inthe .system of the invention;

Fig. A1l illustrates, in tabular form, one arrangement of signal frequency assignments for the first twov digits of a four out of thirty frequency translation,`as may be employedV in the preferred embodiment of applicants invention;

Fig..12 shows the equivalent two-digitvdecimal numbers corresponding to anyV combination of two out of fteenffrequencies when selected in accordance with the table ofV Fig. 11;V and Fig.V 13 shows a Vplan according to which the several sheetsofrdrawings, Fig. 2 through Fig. 10, should be arranged in order properly to trace applicants circuit continuity.

The general operation of the invention will first be explained in terms` of the block diagram The identification of a mobile station Which is signaled by a call originating from the land station will first be described. Referring to Fig. 1, which is a block diagram representing a land stationand one mobilev station, the call is originated by connecting thedial I to the control unit l2. Pulses from dial I are transmitted over lead group IUI through equipment in the control unit, and over lead group |02 to the dial pulse sender shown in block number 3;. VThe pulses are counted for each digit and re- The, transmitter radiates the aforementioned combination of audio frequencies and they are received by the mobile station radio receiver shown in block 5. The receiver detects the four audio frequencies, transmits them over lead group I through equipment in the control unit 'I and over lead group IEI'I to the audio amplifier 8. The voutput cf the audio amplifier is transmitted over lead group its through equipment in the control unit, thence over lead group |99 to a set of 'four wave filters 9. In this preferred embodiment of the invention these filters consist of mechanically tuned vibratingv reeds equipped with contacts which close momentarily when the associated reed is excited by its tuned frequency. The contacts of the four reed vibratorsare connected in series to lead I I. Lead IIIJ is connected to a detecting device in the control unit which, operates when all vfour reedsl are excited by their resonant frequencies. The detecting device, when energized, operates equipment in the control vunit which accomplishes the following:

ya.. Disconnects the input of the audio amplifier from the radio receiver.

b. Connects the reeds in a multiple bridge circuit to the input of the audio amplifier thusv producing an oscillatorv having an output consisting of four frequencies, Aone for each of the reed resonant frequencies.

c. Connects the output of thisl oscillatoruover lead group I I3 toradio transmitter I2 where it is used to modulate. the ltransmit-.ter carrier at the mobile station.

d. Conditions the mobile station to subsequently respond to ringing tone.

This modulated carrieris received and de modulated by radio receiver I3 at the land station and the four audio frequencies thus obtained are transmitted over lead group IIdthrough the con,- trol unit 2, over lead groupfl I5 to the frequency translator I4. Here the combination of four frequencies is translated into a four-digit decimal number. This information'is transmitted over lead groups IIS and. IH toa series of check .con-

tacts on the register relays in the dialpulse sender, If thenumberrobtained f rcnjl the frequency translator agreesv withthe number stored in the register acheck signal-isisentover lead I I8 to the control unit.2V where it .operatesequipment Ywhich removes -the four audio Ifrequencies now connected to-.the transmitter and substitutes for them a distinctive-checktone. l This check tone modulates the land station transmitter carrier. The mobilestation radio -receiver' receives this modulated carrier, demodulateslfit and applies the check tone overA leadrgroup Ito the control unit where it operates equipmentwhich operates the bell Il)I andsignal lamp-|68 -over lead. I I I.`

'i Whenthe mobilesubscriber, removes his hand.- set from the switehhook the control unit: i

r a. Removes the audio amplifier from the oscillator condition.

b. Connects the audio amplifier between the output of the receiver and the mobile subscribers telephone.

c. Connects the radio transmitter to the mobile subscribers microphone.

The removal of the four audio frequencies from the mobile station transmitter causes the equipment in the land station to go into the talking condition.

The identification of the mobile station in the case of a mobile originating call Will now be brieiiy described. When the mobile subscriber removes his handset from the switchhook a signalis sent to the control unit 1 which connects the selector reeds in the oscillator circuit previously described. The output of this oscillator is connected to the mobile transmitter I2 Where it modulates the carrier frequency.

The modulated carrier is received by the land station receiver I3, demodulated, and four audio frequencies transmitted over lead group I I4 to the control unit 2 where they are connected over lead H5 to the frequency translator. As previously described the frequency translator converts the four frequencies into a four-digit decimal number. This number is connected over lead group ||6 to the display circuit |5 which consists of a plurality of lamps arranged to display the number visually. The frequency translator also signals the control unit that it has received exactly four frequencies. This causes the line lamp to light as an indication to the operator that a mobile station call has been originated. It also operates equipment in the control unit 2 which causes a check tone to be connected over lead group |05 to the radio transmitter where it is used to modulate the carrier.

The mobile receiver 6 receives and demodulates this signal, applies the check tone over lead group |06 to the control unit 1, Where equipment is operated which causes the mobile station to go into the talking condition. The land station operator operates her talk key, the identification equipment in the land station is released and the call has been established.

In the above description the number of the calling station was displayed visually. It will be understood that instead of a visual display this information could be used to operate a register for use in an automatic message accounting system, if desired.

A detailed description of the preferred embodiment of this invention will now be given for the case of a call originating at a land station.'

Referring to Fig. 7, when the operator desires to originate a call, she operates dial key I6. The operation of key I6 connects ground over lead to operate relay I1. The operation of key I6 also connects the dial I8 over lead 102 to operate relay |63 in Fig. 2. Operation of relay I1 performs no function at this time. The operation of relay |63 connects ground to lead 20|, which operates the slow release relay I9. which in turn provides olf-normal grounds to permit the pulse counting register relays to function. The pulses generated :by dial I8 in Fig. 7 are transmitted over lead 102 to relay |63 in Fig. 2 which repeats the dial pulses. These repeated pulses are counted in a Well-known manner by the relays in Fig. 2 and connected through the relays in Fig. 3 to operate the particular register relays in Fig. 4 corresponding to the numbers dialed. A detailed descriptionof this :counting transformer 33.

`and registering operation is given in aforementioned copending application Serial No. Y56,186. In addition to the translating contacts on the register relays in Fig. 4 which convert the four digit decimal number into a combination of four audio frequencies, a set of contacts is provided to indicate which relays are operated in the register. These contacts are used to compare the four-digit decimal number produced by the frequency translator of Figs. 8 and 9 with the number originally dialed and to indicate if the two numbers are the same.`

When the operator has completed dialing four digits, leads 40|, 402, 403 and 404 will each be connected through the translating contacts of the relays in Fig. 4 to a distinctive frequency. Leads 40| to 404 are connected to amplifiers 20 to 23, respectively, in Fig. 6. The outputs of these amplifiers are combined through hybrid coils 24, 25, 26. f The combined output of hybrid coil 26 is connected over leads 60| and 602 to contacts of relay 28 in Fig. 7, from thence over leads 103 and 104 and through contacts of relay 29 to leads 105 and 106 which 4are ,connected to the radio transmitter 21. The combination of four tones is used to modulate the carrier frequency of the radio transmitter. This modulated carrier is received by the mobile station radio receiver 30 in Fig. 10. The demodulated output of receiver 30 is con- Vnected over lead |00|l through a normally closed contact on relay 3| to lead |002 which is connected to the input of the audio amplifier 32. The output of the audio amplifier connects to output Lead |003 from the output transformer is connected to one side of the Windings of relaysA 35 to 38, respectively. These relays are of the tuned reed type described in copending applications of I-LC. Harrison, Serial No. 767,487, filed August 8, 1947, and Serial Nos. 776,251, now Patent No. 2,499,581, granted March 7, 1950, and 776,252, led September 26, 1947, now abandoned. The other side of the output Winding of transformer 33 is connected over |004 through a normally made contact on relay 34 and over lead |005 to one side of the windings of coils 39 to 42, respectively. The other side of the Winding of each coil isconnected to the driving coil of its associated relay over leads |006 to |009, respectively. When these relays 35 to 38 respectively, are energized at their resonant frequencies, their vibrating contacts close intermittently. A'positive potential on the voltage divider consisting of resistances 43 and 44 is connected over lead I0|0 through the vibrating contacts of relay 35, lead |0| I, through resistance 48, lead |0|2, through the vibrating contacts of relay 36, lead |6|3, through resistance 46, lead |0|4, through the vibrating contact of relay 31, lead |0|5, through resistance 41, lead |0|6, through the vibrating contacts of relay 38 to lead |0|1 which is connected through a normally closed contact` on relay 3| over lead |0|8 to a grid of vacuum tube 50. Condensers 49, 5|, 52 and 53 are used to bridge over the open periods of the vibrating contacts, maintaining positive potential along the circuit during the intervals when the vibrating contacts are open. When the charge on condenser 49 has become sufliciently positive, plate current is caused to iiow in vacuum tube 50 causing relay 54 to operate.

The operation of relay 54 connects ground to lead |0|9 Vthrough a normally made contact on relay 55 to lead |020 through a normally made contact of .relay 34 over lead `|'02I to operate relay 3|. -The Operation'of relay 3| connects 7 ground'irom a ncrmallymadecontactotamakebefore-breakYspringcQmbinatiQn-onirelay SG-over 'lead m22; te -iead jlozga to lead lim which holds relay 3| operated under control of relay 56. The operation vof relay 8| connects ground lover.y lead 1824130 the transmitter controll circuit 5.1 which turns on the radio transmitter-'58.

Winding V33A ofthe output transformer which is grounded at'its center" tap forms half of a bridge circuit. The other half of the bridgecomprises the four parallel 'circuits eachcomprising a tuned reed relay in series with a balancingcoil Khaving an impedance of such alvalue that-itfbal- "ancesthe impedance ofthe reedrelay-driving coil 'at all frequencies'except the resonant frequency of the reed. vWhen the resonant frequeneyfoia reed is applied to-the bridge,A thereed vibrates and 'its :notional-impedance is reected-by'thefrelay coil thereby limita-lancingI the bridge. For example, if the resonant frequency off relay 35 ais applied to the bridge circuit-in combination rwith several otherfrequencies the resonant frequency ofrrelay -35 vvvill appear onlead |006 and'allother frequencies Willbe greatly attenuated'. Iabridge lof* vthis type s-inserted'in the feedback pathcflan ampliiier having sufficient gain to overcome' the 'mid-,band loss off the bridge',A a4 condi-tionfor Ypro'- 'duing oscillations at vthe-reed frequency will be obtained Joperation is describedjmre ifully 'in copendingV applicationof A, BachelemSerial No. 22,820,1`1ed AApril 23, 1948, now Patent No.

-geiizdgrapped February 13,1951. vniche preferred embodiment :ofthe presentfinverrticn there are fourbalanced reed circuits connectedin pargliel. each having @independent Output The operation. relay .3.1 connects. lead 'i006 through phase.. shifter 15.3. ausi'limtine' resistance 1.| to mixing resistance'12. The amplitude Qfthis Ytvavel islimited bythermistor 6 1. ASimilarls cgleatls [|10 1ste Al U89.;respectively,.are connected.` through Y operated-.Contacts 0f` relay 3..l Athence. through phase ,Shifters .sa :ell .ana tu, respectively. and

jlfimitmg resistors 10. T69 `and 6 8, respectively, thence through the Arrlixing vresistance '12v to ground' The-roltaseideveloped.acrossreslstance l2. transmitted overlegdl028,.thr0ug1h an. Qperatedgccntact of relay'l.. overleed |802, tothe input ciY the audio amplifier .32.. Operation. of

. eiver `3 from the audi@ amvlier. 3.21- The above- 'mobile `station modulator .59, which serves; to

modulate the carrierfrequency. of .the radioffflansmitter 58. The. .modulated carriers. is 1 applied to the transmitter over lead |025. :The opera-tion of relay 3| also transferred theoutput of v.the-.radio receiver from lead |002. to lead. |029. Lead .|029 is appl-ieu to the input of Wavenner. 1s, the 01nvof the tuned .reed type.

8 ated con-tact of :relay 3|. and lead z|f|l|s8 to. agrld of vacuum tube 5|).

The modulated ycarrier is received by the land station receiver '15 in Fig. 7. 4The demodulated output of this receiver, comprising the. fourv tones generated by the mobile station equipment, is connected over leads 101 and 108 through normally `closed contacts of relay 29 over leads 108 and 1&0 to Fig. 8. Relays 8.1 to 88 in Fig. 8l are connected across leads 1.09 and 1|D, as are relays 89 to 95 in Fig. 9. Relays 8| to 95 inclusive, are These relaysV 8| to 95 serve .todetect tWo of the four signal frequencies vfrom the mobile station and to translate them intoitwodecimal digits representing the rst two ofwa four digit number. VLeads 109 and 11|) also 4are connected to block :1.6. inFig. 8. Whichrepre- Vsents anotherunit.exactlyflike the rest of Fig. 18 exceptthat the eight reed relays vin .block 16 are tuned to respond to different frequencies. Similarly, block `11 in Fig. 9 represents a circuit exactlylike vthe main part of Fig. 9. The circuit in blocks 16. and 11 is used to detect the two. Signal frequenciesr representing thelast two digits of a four digit number.

In order-'better .to understand the Yoperation of Figs and 9, let us assumethat the operatorhas dia-ledfthe number 29.7.3. As can be seen from the chart of Fig. 11 this number isrepresented by F2 and F1 of the first. group of *l5 frequencies and FlfandFt-S of the second group. of 15 frequencies.

It is to ibe understoodthat the fifteen frequency tones :in .the second group are rentirely different from :the -iteen tones of the frst group, so that aI total of thirty different frequencies are available. Thus theselectedatones of the second group which We read off the. chart .of Fig. 11 as F1 and `F|31might be distinguished from the tones of the. rst group by considering the second pair as .F1-ie t5. and Fielfl. YFor `brevity of circuit .description We here trace. indetal the course of the rstpair of selected tones only, it being understood that .the remaining pair of tones follow :similar courses through identical circuits contained injblocks .16.and 't1 ofFigs. 8 and 9; and |.55lof Fig. Li. The first two of these frequencies, F2 and F1. applied to leads 1,89 and 1|0 Awill-.cause thesecond and seventh relays, :8.2 and 8.1 to Vibrate. When relay82 vibrates, ground is` applied ;to. lead intermittently causing condenservil to discharge. through resistance 19. When condenser 88 dis-charges sulciently from its previous negative condition, Vacuum tube 9BY becomes conducting and cau-ses relay 91, which is in its plate circuit, tooperate, .Relayi91 operated locks. to a ground on lead 882 which is controlled by. a normally closed contact. on relayr29 in Fig. 7. Similarly, relay 8.1 causes vacuum tube 98 to become ,conducting and operaterelay 99 which also locks :to ground on lead 882. Similarly, in block 18 a ...example here illustrated ground connected :through va normally made contact of relay |38 in Fig.' 8 to lead 8|;6, through an operated contact '70.

of relay :91 tolead 8,|1,j through a normally closed contact .ofrelayll to'lead 805, through a normall-y; closed contact of relay |32 to lead 806,

ithrough `a normally closed contact of relay|33 to leadll'h through normally closed contact of; relay |;34:;to; lead: 8.0.8, throughsan operated' contact of relay 99 to lead 809,`through a normally closed contact of relay |35 to lead 8 I 0, and thence to Fig. 9. In Fig. 9 lead 8 I 0 connects through a normally made contact of relay |36 to lead 90|, through a normally made contact of relay |31 to lead 902, through a normally made contact of relay I 38 to lead 903, through a normally made contact of relay |39 to lead 904, through a normally made contact of relay to lead 905, through a normally made contact of relay |40 to lead 906, through a normally made contact of relay I4| to lead 901 and thence to Fig. 8. In Fig. 8 lead 901 is lconnected through a similar contact network in block 10 over lead 8|2 to block 11 in Fig. 9, through a 'similar contact network to lead-908 to block 16 in Fig. 8. In block 16, lead 908 connects to lead 8II which operates relay |42 in Fig. 7.

The operation of relay |42 connects ground to lead 126 thence through an operated contact of relay I1 to lead 121 and on to Fig. 4. AFor the first two digits of the number used in the present example, relays |44, |54 and |50 will be operated. Lead 121 is -connected through a normally closed contact of relay |48 to lead 405, through an operated contact of relay |44 to lead 406, thence to Fig. as lead 50|, thence to Fig. 9 as lead 909, thence in Fig. 8 through an operated contact of relay 91 to lead 803, thence through an operated contact of relay 99 to-lead 804, thenceas lead 9|1 to Fig. 9, thence through a normally closed contact of relay |4I to lead 9I6, thence through a normally closed contact of relay |40 to lead SI5, thence through a normally closed contact of relay |00 to lead 9I4, thence through a normally closed contact of relay |39 to lead 9I3, thence through a normally closed contact of relay ISB to lead 9I2, thence through a normally closed contact of relay |31 to lead 9II, thence through a normally closed contact of relay |36 to lead 3M and back to Fig. 8. From lead 8I4 of Fig. 8 through a normally closed contact of relay |35 to lead 8I3, thence through an operated contact of relay 99 to lead 9I0 of Fig. 9, lead 502 of Fig 5, and to lead 408 of Fig. 4. From lead 408 of Fig. 4 through an operated contact of relay |50 to lead 401, thence through an operated contact of relay |54 to lead 1I I. From lead 1| I in Fig. 7 through an operated contact of relay vI1 in Fig. '1 to lead 1| 2, thence through an operated contact of relay I1 to lead 1|3 and back to block |55 in Fig. 4. In block |55 lead 1I3 is connected through a contact network on the tens register relays similar to the checking network already described for the thousandths register ycomprising relays |43 to |48. In a manner similar to that described above this lead is connected through the operated relays in the register circuit of block |55, thence through blo-ck |56 in Fig. 5 which is similar to one of the lamp blanks shown in the main part of Fig. 5 as |64 and |65, through the frequency translator for the tens unit in block 11 of Fig. 9 and block 16 of Fig. 8, back through block |51 in Fig, 5, thence through block I 55 in Fig. 4, going out on lead 1| 4 to Fig. '1. Lead 1|4 is connected through an operated contact of relay |1 of Fig. 7 to lead 1I5 to operate relay 28. The operation of relay 28 connects ground to lead '|24 causing lamp |60 to light as an indication to the operator that the called station has been reached. The operation of relay 28 also connects the output of the check tone oscillator block |58 over leads 1|6 and 1I1 to leads 103 and104 which are connected through normally closed contacts of relay 20 to leads 105 and 106 leading to transmitter 27. The check tone oscillator 158 l0. may be any type of ,signal generator, of which many types are well known to the art.

The demodulated output of radio receiver in Fig. 10, comprising the received check tone, is connected from lead IO0I through an operated Contact of relay 3| to lead |029 thence through the wave lter 13, which is a narrow band lter of any type common to the art, thereby passing the check tone over .lead |030 to rectifier 14 which is poled in a direction to pass positive voltage peaks only. The rectified output from rectifier 14 is connected over lead I03| through an operated contact of relay 3| to lead I0|8 and thence to a grid of tube 50. The network consisting of resistance 43 and capacitance 49 smooths the output of the rectiiier and maintains a steady voltage on the grid of tube 50.

When relay 3| iirst operated as described above, it removed the positive potential from the grid of vacuum tube 50, cutting off its plate current and causing relay 54 to release. Relay 54, released, connected ground to lead |032, thence through an operated contact of relay 3| over lead |030 to operate relay 55. Relay in operating connected ground to lead |032 to hold itself operated under control of relay 3|. When relay 54 reoperates as a result of the. received check tone it connects ground to lead I0 I 9 thence through an operated contact of relay 55 and lead |034 to operate relay 56. VThus it will be apparent that the second successive operation of relay 54, under these circumstances, conditions the mobile station to respond to a ringing signal. The operation of relay 56:

a. Substitutes a controlled ground on lead |035 from an operated Acontact on relay 54 for the locking ground for relay'3I.

b. Locks itself over lead |036 to ground through an operated contact of relay 3|.

c. Applies a ground tolead |031 through a normally closed switchhook contact over lead |038 'to operate the call bell |043 and the call lamp |044 through lock-up relay |045.

If the mobilev subscriber isnot in attendance at his mobile station when an incoming call is received, the' call lamp |044 remains operated through the lock-up device |045 to indicate to him that a call was received during his absence. As has been described above, the land station operator has already receivedpositive indication that the mobile station was signalled regardless cf whether the mobile subscriber is in attendance at his mobile station when the call is made. The indicating call lamp |044 at the mobile station may be extinguished by the'mobile subscriber at any time by operation of push button |046, or it may also be controlled by a switchhook contact so as to be extinguished When the subscriber lifts his handset from the cradle.

Assuming that the mobile subscriber is present to answer the incoming call, when the subscriber lifts his handset from the cradle,jthe switchhook |61 operates, connecting ground to lead |039 through an operated contact of relay 55 to operate relay 34. The operation of relay 34 removes ground from lead |02I releasing relay 3|. The release of relay 3| removes the reed relays 35, V36,31 and 38 from the oscillator circuit. The release of relay 3| releases relay 55, and also removes the outputof audio amplifier 32 from rectier 14 thereby cutting off the plate current oivacuum tube 50 and releasing relay 54. Operation of relay 34 further connects the output of the audio amplifier 32 to the receiver of the subscribers handset over lead |040. It also ateatro? 1'1. connects the subscribers microphone over lead |04| through an operated contact of relay 34ove'r lead |021 to the modulator'59. Relay 34 remains locked up over lead |042 through the operated contact of relay 34 overlead V|939 to ground on the operated switchhookcon-tact. The 'operation of the switchhook l|61 also silences theV bell by interrupting the circuit between |031 and |038. VThe mobile station is now in the 'talking condition with all signalling equipment released.

When the operator is satisned that the call has been established, as shown by the oper-ation of a lamp at. her switchboard, she releases Key |'6 and operates key |59 which connects ground to lead 1|6 operating relay 29. The operation of relay 29 connects leads 105 and 106 Vto 'the'hybrid coil |6| over leads '1 |'8 and 128. The output of the hybrid coil is connected through the line jack |60. The operation o'f relay 29 also 'connects the radio receiver over leads 101 and T00 L through operated contacts of 'relay 29, via leads 'H9 and |20 to the'hybrid coil Il, thus establishing a ta king path atthe land station. The operation of relay 29 removes ground from lead 802 causing the release of all previously operated relays in Figs. -8 and r9.

When the operator releases key I6 breaking the connection between the dial |`8 and 'relay |63 in Fig. 2, the latter releases causing the release of slow release relay I9. The release of 'relay |9 releases all operatedrelays 'in Figs. 2, 3 and 4. At the end of the call the operator releases key |59 releasing relay 29 in Fig'. l which releases all equipment in the land station, restoring idle condition preparatory to the placing of another call. VThe mobile subscriber when he hangs up at the end of the call releases all relays in the mobilestation which is vthen in condition to receive or initiate a new call. y

lThe case'where a call is originated by va mobile station will now be described.

When the subscriber removes his handset from the switchhook |61, ground is connected through an operated contact of 'the switchhook |61 to lead |020 through a normally closed contact of relay 34 over lead |02| to operate relay 3|. The operation of relay 3| as previously described sets up the tuned reed relays 35-38 and the audio amplier 32 as a four tone oscillator. The operation of relay 3| connects ground from a normally closed contactV of relay 54 and lead |032 through an operated contact of relay 3| to lead |033, to operate relay 55. The operation of relay 3| also energizes the mobile radio transmitter 58 over lead |024. VThe four frequencies from the mobile station tuned reed oscillator 'are vthus transmittedV as previously described. This signal comprising in combination four distinctive tones fromthe mobile station is received and demodulated by the land station radio receiver 15 in Fig. '1. The outputof receiver 15 is connected over leads 101 and 108 through normally closed contacts of relay 29 tor leads 109 and 1|0 and thence to the frequency translator in Figs. 8 and 9. As previously described, these four signal operatortnatxa.' mobiie ,station has originated a call.V In this case of la call originating from a mobile station, relay |1 of Fig. 7 does not operate, 'as previously, and therefore ground s connected through normally closed contacts on this relay "to 'leads 804 and 815. Ground on lead 804 from Fig'. l'7 goes 'through the contact network on relays 1in Figs. Sand 9. Assuming the same number used previously, that is, 2973, ground is connected from lead 804 through an operated contact o'f relay 99 in Fig. 8 to lead 803, thence through 'an operated contact -of relay 91 to lead 909, thence toFig. 19, thence 'becoming lead 55| in Fig. l5 to lightlainp |64 of Fig. -5 thereby indicatingthe 'thousands digit. Ground on lead 854 from 8 is connected to lead 9|1 in Fig. 9 through 'alncirmally closed contact on relay |4| tok lead '916, thence through av normally closed contacten relay |40 to lead 9|5, thence through a normally closed vContact on relay |00 to lead 914, 'thence/through a normally closed Contact on relay |39 to lead 9|3, thence through a normally closed 'contact on relay |38 to lead 9|2, thencev through fa lnornflally closed contact on relay u|31 to A"lead 9H, thence through a normally closed contact on relay |36 to lead 8|4 and back to Fig. 8, thence 'through a normally closed contact on relay l|"3`5fto Ylead 8|3, Athence through an operated contact on 'relay 99 to lead 9|0 and back againto Fig. v9.

In Fig. oleada-lo connects to lead 5oz of Fig. 5, thereby lighting lamp |65 to indicate the hundreds digit. Similarly the 'proper lamps for indicating the tens and units digits are lit by operation of carrespond'ing relays in blocks 16 and 11 of hfand 39. When relay |42 in Fig. '1 operated, it connected ground from lead 123 via a normally closed contact on relay |1 through an operated Ycoritacton relay |42 to lead 1|5, thereby operating 'relay 28. The operation of relay 28 as previously described connects the output of the check tone oscillator |58 to the radio transrhitter through normally closed contacts on relay 29. The check tone when received at the mobile station in Fig. -10 again passes through filter 13 andrectier Mito cause vacuum tube 50 to draw plate current, thereby operating relay 54. In a manner similar to that 'previously described, the operation of relay 54 causes the operation of the call relay 53.

i v'The'operation of relay l56 in turn operates relay 34` as previously described. The operation of relay -34 causes the release of relay 3 l. With relay 34 operated and relay 3| released, the mobile station isfset i-n the talking condition.

)When Vthe operator has recorded the number of theA calling -nobi'le station as indicated by operation 'of the identifying display lamps at her switchboard, she yoperates key |59, thereby operating relay 29 in Fig. 7. The operation of relay I29 inwFigg? releases the Vlocked up relays in Figs. 8 and 9 causing'4 the display lamps in Fig. 5 to be extinguished. Disconnection at the end of the call is accomplished in the same manner as in thevcasevof 'a land station originated call described above.

What is claimed is:

l. In 4a bidirectional radio telephone multiparty vselective signalling system, a party identication larrangement comprising a distinctive combination of tuned signal generators at each party station, Ame'ar'is for simultaneously energizin'g a `plurality of said signal generators at any party station, and receiving means at a calling station responsive to signals from said ener- 13A gized generators at any party station, said receiving means adapted to identify selectively any party station in accordance With the distinctive combination of signals received therefrom.

2. In a bidirectional radio telephone multiparty station signalling system, a party identii'lcation arrangement comprising a distinctive combination of tuned signal generators at each party station, means at any party station for simultaneously energizing said signal generators thereat, and receiving means at a calling station responsive to signals from said energized generators at any party station, said receiving means adapted to identifysaid party station selectively in accordance with the distinctive combination of signals received therefrom.

3. In a bidirectional radio telephone multiparty station signaling system, a party identication arrangement comprising a distinctive combination of tuned signal generators at each party station, means at a calling station for energizing all of said signal generators at any party station simultaneously, and receiving means at said calling station responsive to signals from said simultaneously energized signal generators, said receiving means adapted to identify any party station in accordance with the distinctive combination of signals received therefrom.

4. In a multiparty station signalling system, a calling station and a plurality of outlying stations interconnected with each other and with said calling station by a common transmission medium, said outlying stations each comprising a plurality of tuned elements adapted to be energized by a particular combination of signals in accordance with a predetermined code and not to be energized by any other combination, means at said calling station for generating simultaneously a plurality of distinctive signals in any desired combination, means including said plurality of tuned elements at each outlying station controlled by reception thereat of a particular combination of simultaneous signals corresponding to the code of said station for generating a plurality of simultaneous signals distinctive to said outlying station, further means at each outlying station for transmitting said generated plurality of distinctive signals to said calling station, receiving means at said calling station responsive to said transmitted signals from said outlying station, and further means at said calling station adapted to identify said outlying station by the distinctive combination of signals received therefrom.

5. In a multiparty station signaling system, a common transmission medium, a calling station and a plurality of outlying stations interconnected with said calling station by said transmission medium, each of said outlying stations comprising a plurality of tuned relays, adapted to be operated by a distinctive combination of signaling tones in accordance with a predetermined code, means at said calling station for simultaneously generating a plurality of distinctive signal tones in any desired combination, means including said tuned relays at each outlying station controlled by simultaneous reception thereat of a particular combination of signaling tones corresponding to the code of said station for generating simultaneously a plurality of signal tones distinctive to said outlying station, further means at each outlying station for transmitting said simultaneously generated plurality of distinctive signal tones to said calling station, re-

ceiving means at said calling station responsive Y 14 to said transmitted signal tones from said outlying station, and further means at said calling station adapted to identify said outlying station by the distinctive combination of signal tones received therefrom.

6. In a signaling system, a calling station and a plurality of outlying stations interconnected therewith by a common transmission medium, means at said calling station for generating a plurality of digital impulses corresponding to digits of a call number, means for registering all the digits of said call number, a plurality of signaling tones of distinctive frequencies, a translator controlled by said registering means for selecting a distinctive combination of said signaling tones corresponding to the particular call number registered, means for transmitting said selected combination of signal tones from said calling station, means at said outlying stations for receiving said signal tones, selective means at each outlying station responsive to a particular combination of tones received in accordance with a predetermined code for each station, said selective means adapted to generate a distinctive combination of identifying signal tones at any called outlying station, means at said called station for transmitting said distinctive combination of identifying signal tones therefrom, selective means at said calling station for receiving said transmitted signal tones from said called outlying station, means at said calling station for comparing the signal tones received thereat with the signal tones transmitted therefrom, further means at said callingstation operable only upon correct comparison of said signalingtones to interrupt transmission of signal tones therefrom and to establish a talking condition, and means at said called outlying station responsive to interruption of said signaling tones to establish talking condition thereat.

7. In a signaling system, a calling station and a plurality of outlying stations interconnected therewith by a common transmission medium, means at said calling station for registering the digits of a call number, a plurality of signaling tones of distinctive frequencies, a translator controlled by said registering means for selecting a combination of said signaling tones corresponding to the particular call number registeredf means for transmitting said selected combination of signal tones simultaneously from said calling station, means at said outlying stations for receiving said simultaneous signal tones, selective means at each outlying station responsive to a particular combination of simultaneous tones in accordance with a predetermined code for each station, said selective means adapted to retransmit a distinctive combination of identifying signal tones from said called station, means at said calling station for receiving said retransmitted signal tones from said called outlying stations, a plurality of selective means at said calling station for registering said received signal tones from said outlying stations, means at said calling station for comparing said registered signal tones received thereat with the signal tones transmitted therefrom, further means at said calling station operable only upon correct comparison of said signaling tones to interrupt transmission of signal tones therefrom and to establish transmission of ringing tone, means at said called outlying station responsive to said ringing tone to interrupt transmission of said identifying signal tones therefrom and to establish a talking condition thereat, and means at said callateaoav ing station. tofinterruptfsaid ringing tone and said calling station, comparing said retransmitted signal tones from said called station with said, originally transmitted signal tones from said calling station, ahdestablishing a talking condition betvveensaid calling station and said called station only upon exact comparison of said retransmitted signal tones with said originallyv transmittedY vsigr'ialjtones.

9. AIn a multistation selective signaling system, a plurality of outlying 'stations capable of being called, a calling station, a channelof transmission at least in part connecting said calling station with each of Said plurality of stations, each of said plurality of stations being provided with a plurality of resonantly responsive devices selectively operable by alternating current of characteristicindividually unique for each out.-

lying station, means including an emitter at the y calling stationemissive of current of said unique characteristic of one out oisaid outlying stations to be called,means controlled by said resonantlyV responsive devices upon their selective response at one ofsaid outlying stations to said current, generating means at said one station, meansy whereby said generating means is caused to emit to. said calling station current of characteristic uniquely determined for said one station with respect to each and every. of said stations., interconnections whereby said resonantly responsive devices determine said characteristic, and means selectively responsive to verify at said calling station the receipt of current having the characteristic individual to said one station to be called. Y

10. In a multistation selective signaling systern, a calling station, a plurality of stations capable of being called selectively, means for emitting from the calling station toward said plue rality of stations current having a combination of frequency components individual to each station to be called, selectively responsive resonant responders at each station responsive only to the combination individual to that station, and current emitters controlled by selective response of said responders for emitting current of the frequency components which caused response of said responders toward and to said calling station.

1l. In a multistation selective signaling system, a calling station, a plurality of stations capable of being called selectively, means for emitting from'the calling station toward said plurality of stations current having a combination of frequency components individual to each station to be called, selectively responsive resonant responders at each station responsive only to the combination individual to that station, current emitters at said stations controlled by selective response of said responders for emitting current of the frequency components which caused response of said responders toward and to said calling station, comparison means at said cau- Ving station for comparing the combination of frequency components ofthe received current with the frequency components of said current emittedY fromsaid calling station, and a checker operable indifferent Ways accord-ing to the determination of identity "o'r lack of identity by said comparison means.

l2. In lammultistat-ion Vselective signaling system, a calling station, a plurality of stations capable of being called selectively, means for emitting from the' calling station toward said plurality of stations current having a combination of frequency components individual to each Stationto be called, selectively lresponsive resonant responders at 'each station responsive only to the combination individual to that station, current emitters at 'each station controlled by selective response 'off said responder-s for emitting current of the Yfrequency 4components which caused response of said responders toward 'and to said calling station, comparison meansY at said calling station for comparing the combination of frequen'cy components of the received current with the frequncy components of said current emitted from 'said'callin'g station, 'a checker operable in different Ways according to the determination of identity or lack of identity by said comparison means, and fa veriic'a "on current transmitter re- SpoiosiveA to deter" ation of identity by said checker 'for sending 'a vermoeden current to saidV outlying station 'which emitted the incoming current to` be checked, and a call device at said outlying station responsive to said verication current for establishing a calling condition therat.

' 13, In 'a multistatici selective signaling system, a 'calling station, a 'plurality of stations capable of being caIledsclcctiveIy, means for emitting from 'the calling station 'toward said pluralitl7 of station-s current havinga combination of frequency components individual to each station to beY called, selectively responsive resonant responders 'at 'each station responsive only to the combination i'dual to that station, means controlled by response 'of 'said resonant responders to condition said sta on ff'or receiving a verification signal, current e troneo by selective iesponse of said responders for emitting current of 'the frequency components which caused 'response of said responders toward and Vto said calling station, comparison means at said calling station for comparing the combinationof frequency components of the current received thereat with the frequency components of 'said `c`1rrrtint ern'itted from said calling station, Va Acher-lter operable in diierent Ways according to the determination of identity Yor lack of identity by said comparison means, and a verification 'signal transmitter responsive to determination oi identity by said checker for sending a verification current to said outlying station which emitted the incoming current to be checked, and a call device at said outlying station rresponsive to said vrification current for establishfincr ac :alling condition thereat.

14. A station identifying arrangement for signaling systems comprising a calling station 'and 'a plurality ot outlying stations, said outlying statons each comprising a distinctive plurality 'of diiierently tuned receiving means, sepa-v rateman's controlled by simultaneous operation oi all t said receiving means at an outlying station to esta'onsh a calling condition, means at -a 'calling station for selecting a simultaneous 'plurality f calling sigalsrcorrespohdllg in frequencies to the individual tunings of said plurality of tuned Vreceiving means at an outlying station to be called, means for causing the simultaneous transmission of said selected calling signals to all of said outlying stations, means at one of said outlying stations including said distinctive plurality of differently tuned receiving means responsive to said calling signals to establish a calling condition at said station, means for causing return transmission of a corresponding simultaneous plurality of signals from said called outlying station to said calling station upon reception of said calling signals at said outlying station, receiving means at said calling station responsive to said return signals from said outlying station, and means for identifying said outlying station thereby.

15. A signaling system including a calling station and a. plurality of outlying stations each comprising a distinctive plurality of individually tuned elements adapted to be actuated by electrical waves of frequencies corresponding to their respective tunings and not to be actuated by waves of any other frequencies, means at a calling station for generating simultaneously a plurality of electrical waves corresponding in frequencies to the respective tunings of elements at :an outlying station, means for causing the transmission of said waves to and their reception at an outlying station, means at said outlying station controlled by the actuation of distinctively tuned elements thereat to return a distinctive signal from said outlying station to said calling station, and indicating means at said calling station responsive to said returned distinctive signal to identify said outlying station.

16. A signaling system including a calling station and a plurality of outlying stations each comprising a differently tuned selector adapted to be operated by a simultaneous combination of electrical currents of distinctive frequencies and not to be operated by any other combination, means at a calling station for selecting and simultaneously combining a plurality of calling currents of frequencies distinctive to the tuned selector at any outlying station to be called, transmitting means at said calling station, a transmission medium connecting said calling station with said plurality of outlying stations, receiving means at each of said outlying stations, further transmitting means at each outlying station in combination with said selector means thereat for transmitting a distinctive return signal therefrom upon the reception of a distinctive call signal to operate said selector means thereat, means at said calling station for receiving said distinctive return signal as transmitted from said outlying station, and indicating means at said calling station controlled by reception thereat of said return signal from said outlying station to indicate that said outlying station has been signaled.

17. In a multiparty station signaling system, a calling station and a plurality of outlying stations interconnected therewith by a common transmission medium, said outlying stations each comprising a plurality of tuned vibrator elements in combination with means for vibrating said elements when said means are energized by a plurality of distinctive signals of frequencies corresponding to the vibratory period of said elements, means at said outlying stations including said vibrator elements for generating a distinctive combination of signal tones when said elements are vibrated, means at said calling station for transmitting simultaneously a distinctive plurality of calling signals selected in accordance with an assigned code to call any of said outlying stations, selective receiving means at an outlying station including tuned vibrator elements adapted to be vibrated by reception of said selected cornbination of signals from said calling station, means at said outlying station operable incident to the simultaneous vibration of said vibrator elements to generate said distinctive combination of signal tones thereat, means for transmitting said generated signaltones from said outlying station to said calling station, means at said calling station for receiving said transmitted signal tones from said outlying station, means at said calling station for comparing said received signal tones from said outlying station with said calling signals transmitted from said calling station to said outlying station, further means at said calling station operable by comparison of said received signal tones and said transmitted calling signals to interrupt said transmitted calling signals from said calling station and to impress on the transmitting means thereof a distinctive ringing signal, and means at said called outlying station responsive to said ringing signal to effect a calling indication thereat.

FERDINAND S. ENTZ. ROBERT O. SOFFEL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,196,761 Clausen Sept. 5, 1916 1,532,207 Stacy Apr. 7, 1925 1,608,520 ONeill Nov. 30, 1926 2,052,581 Richards Sept. 1,1936 2,057,541 Shepherd Oct. 13, 1936 2,057,656 Bauer Oct. 20, 1936 2,139,352 Boswau Dec. 6, 1938 2,168,602 Hassan Aug. 8, 1939 2,188,520 Wochinger Jan. 30, 1940 2,206,538 Rhodes July 2, 1940 2,232,866 Pruden Feb.` 25, 1941 2,315,798 Leibe Mar. 30, 1943 2,340,798 Deal Feb. 1, 1944 2,393,291 Clark Jan. 22, 1946 2,444,452 Labin July 6, 1948 FOREIGN PATENTS Number Country Date 516,615 Great Britain Jan. 8, 1940 OTHER REFERENCES AIEE Technical Paper 49-100, December 1948, 

